1. Field of the Invention
This invention relates to a cross-connect switch for fiber-optic communication networks including wavelength division multiplexed (WDM) networks, and more particularly to such an optical switch using a matrix of individually tiltable micro-mirrors.
2. Description of the Background Art
Multi-port, multi-wavelength cross-connect optical switches with charactedstics of large cross-talk rejection and flat passband response have been desired for use in wavelength-division multiplexed (WDM) networks. Four-port multi-wavelength cross-bar switches based on the acousto-optic tunable filter have been described (“Integrated Acoustically-tuned Optical Filters for Filtering and Switching Applications.” D. A. Smith, et al., IEEE Ultrasonics Symposium Proceedings, IEEE, New York, 1991. pp. 547-558), but they presently suffer from certain fundamental limitations including poor cross-talk rejection and an inability to be easily scaled to a larger number of ports. Attempts are being made to address this problem by dilating the switch fabric, both in wavelength and in switch number, to provide improved cross-talk rejection and to expand the number of switched ports so as to provide an add-drop capability to the 2×2 switch fabric. This strategy, however, adds to switch complexity and cost. Recently, Patel and Silberberg disclosed a device employing compactly packaged, free-space optical paths that admit multiple WDM channels spatially differentiated by gratings and tenses (“Liquid Crystal and Grating-Based Multiple-Wavelength Cross-Connect Switch,” IEEE Photonics Technology Letters, Vol. 7, pp. 514-516, 1995). This device, however, is limited to four (2×2) ports since it relies on the two-state nature of polarized light.